code quality: remove unreachable break; from allsites case in network/sites.php

[justlevine]

This PR removes an unreachable break; from the 'allblogs' -> 'delete' case in wp-admin/network/sites.php, as the line before exits entirely.

While this issue was surfaced via PHPStan in #7619 (trac: https://core.trac.wordpress.org/ticket/61175 ), it can be remediated independently of that ticket.

Trac ticket: https://core.trac.wordpress.org/ticket/63268

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[johnbillion]

I believe this is a stylistic choice, so every case always has a break unless it intends to fall through. Whether or not that's documented or enforced in the coding standards I am not sure.

[justlevine]

Whether or not that's documented or enforced in the coding standards I am not sure.

It's a PHPStan level-4 violation, so while there's 0 pressure to get this merged, whoever is deliberating on the stylistic argument should keep in mind that once we hit that level this will look like:

...
	require_once ABSPATH . 'wp-admin/admin-footer.php';
	exit;
break; // @phpstan-ignore deadCode.unreachable (Optional comment about how this was a stylistic choice )

	case 'spam':
...

PS: there are other parts of the codebase where a custom $this->exits(); will need a break; to prevent WPCS from reformatting the subsequent case statements. That's not the case here and won't be needed elsewhere either once PHPStan (annotations) are merged, and we can start using the @never type to indicate an exit.

E.g.

wordpress-develop/src/wp-includes/html-api/class-wp-html-processor.php

Lines 2107 to 2115 in 3277cd6

	$this->bail( 'Cannot process elements after HEAD which reopen the HEAD element.' );
	/*
	* Do not leave this break in when adding support; it's here to prevent
	* WPCS from getting confused at the switch structure without a return,
	* because it doesn't know that `bail()` always throws.
	*/
	break;
	/*